Monday, 16 July 2012
· The extensor tendons to the four fingers pass across their respective metacarpophalangeal joints.
· The deeper fibres of the tendons form the posterior capsule of the joints.
· The bulk of each tendon passes freely across each joint.
· The tendons then broaden out and divide into three slips on the dorsal aspect of each proximal phalanx.
· The central slip passes on to the base of the middle phalanx.
· The lateral slips diverge around the central slip and receive strong attachments from the interossei and lumbricals forming the extensor expansion.
Boutonnière (“button hole”) deformity:
· Injury to the central tendon results in an imbalance in the extensor mechanism.
· Flexor digitorum superficialis is unopposed and it flexes the proximal interphalangeal joint.
· This forces the head of the proximal phalanx between the lateral bands.
· With time, the triangular ligament ruptures causing the lateral bands to displace volar to the axis of motion of the proximal interphalangeal joint and become flexors of the joint.
· The extensor hood retracts proximally, causing extension at the metacarpophalangeal and distal interphalangeal joints.
· This results in flexion of the proximal interphalangeal joint and hyperextension of the distal interphalangeal and metacarpophalangeal joints, known as the boutonnière (“button hole”) deformity.
· Types of injury:
1. Avulsion fracture of middle phalanx
2. Partial rupture with stretching of central slip
3. Complete rupture with seperation
Reference : Ultrasound imaging of finger tendons at the bedside in the emergency department, Southern Cross University ePublications@SCU.